Kinetic Resolution of α‐Silyl‐Substituted Allylboronate Esters via Chemo‐ and Stereoselective Allylboration of Aldehydes

Park, Jin‐Young; Jung, Yongsuk; Kim, Jeongho; Lee, Eunsung; Lee, Sarah Yunmi; Cho, Seung Hwan

doi:10.1002/adsc.202001170

Cited by 17 publications

(26 citation statements)

References 60 publications

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“…This protocol affords chiral allylic gem ‐silylboranes efficiently, which are a valuable class of stable gem ‐bimetallics reagents [11] that could enable multi‐fold functionalization, allowing efficient construction of molecular complexity. To date, only two highly enantioselective catalytic methods to prepare allylic gem ‐silylboranes have been reported, including asymmetric homologation reactions of alkenylboronic derivatives with trimethylsilyldiazomethane, [12] and kinetic resolution of allylic gem ‐silylborates [13] . Both these known methods could only afford chiral γ‐mono‐substituted gem ‐silylborons, while chiral γ,γ‐disubstituted allylic gem ‐silylborons remain unexplored.…”

Section: Methodsmentioning

confidence: 99%

“…Bisoxazoline ligands bearing a benzyl group (L6, L7, L8, and L9; entries 7-10) [16] gave promising results, with ee values up to 53 %. The choice of solvent had a remarkable impact on the enantioselectivity (entries [11][12][13][14]. In benzene, the highest ee was obtained (entry 14), but the yield was only moderate, probably because of the poor solubility of the Cu I •L8 complex.…”

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confidence: 99%

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Highly Regio‐, Stereo‐, and Enantioselective Copper‐Catalyzed B−H Bond Insertion of α‐Silylcarbenes: Efficient Access to Chiral Allylic gem‐Silylboranes

et al. 2022

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Herein, we report the development of a method for highly regio-, stereo-, and enantioselective BÀ H bond insertion reactions of α-silylcarbenes generated from 1-silylcyclopropenes in the presence of a chiral copper(I)/bisoxazoline catalyst for the construction of chiral γ,γ-disubstituted allylic gem-silylboranes, which cannot be prepared by any other known methods. This reaction is the first highly enantioselective carbene insertion reaction of α-silylcarbenes ever to be reported. The method shows general applicability for various 3,3disubstituted silylcyclopropenes and exclusively affords E-products. The novel chiral γ,γ-disubstituted allylic gem-silylborane products are versatile allylic bimetallic reagents with high stability and have great synthetic potential, especially for the construction of complex molecules with continuous chiral centers.Carbenes are important intermediates with diverse reactivities. α-Silylcarbenes are a class of functionalized carbene species with relatively good stability, [1] and their asymmetric transfer reactions constitute a promising tool for facilely introducing the silyl-methylene moiety and preparing structurally diverse chiral organosilanes. [2] α-Carbon carbenes were broadly utilized in the enantioselective carbene transfer reactions; [3] however, the analogue carbene transfer reactions of α-silylcarbenes are much underdeveloped probably owing to the restricted source of α-silylcarbene precursors [4] and the lack of efficient catalytic protocols (Scheme 1a). Dirhodium or copper-catalyzed asymmetric cyclopropanation reactions of α-silylcarbenes derived from corresponding α-silyl diazocompounds provided a reliable access to chiral silylcyclopropanes, [5] yet highly enantioselec-tive insertion reactions of α-silylcarbenes are basically unknown. [6] Recently, our group developed a method of coppercatalyzed BÀ H insertion reaction of cyclopropene-derived αvinylcarbenes. [7] We hypothesized that 1-silylcyclopropenes might serve as a suitable precursor for α-silyl-αvinylcarbene, [8] which could undergo enantioselective BÀ H insertion to afford chiral gem-silylboranes (Scheme 1b). To achieve this transformation, at least the following three challenges need to be addressed. ( 1) We needed to regioselectively cleave the C1-C3 bond to form an α-silyl-α-vinyl metal carbene intermediate in the ring-opening process. [9] (2) We need to control the stereoselectivity of the C=C bond if R 1 and R 2 were different. (3) We needed to achieve efficient chiral induction to control the enantioselectivity of the BÀ H bond insertion. [10] By using a Cu I /chiral bisoxazoline complex, we established a method for highly regio-, stereo-, and enantioselective BÀ H bond insertion reactions of α-silyl-α-vinylcarbenes derived from 1-silylcyclopropenes, representing the first highly enantioselective XÀ H bond insertion reaction of αsilyl-substituted carbenes. This protocol affords chiral allylic[*] M.

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Section: Methodsmentioning

confidence: 99%

mentioning

confidence: 99%

Highly Regio‐, Stereo‐, and Enantioselective Copper‐Catalyzed B−H Bond Insertion of α‐Silylcarbenes: Efficient Access to Chiral Allylic gem‐Silylboranes

et al. 2022

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“…Recently, Cho and co-workers reported the kinetic resolution of α-silyl-substituted allylboronic esters via CPA catalyzed chemo-and stereoselective allylation of aldehydes (Scheme 25). [36] In the presence of catalyst (R)-CPA-3, the addition reaction between racemic α-silyl-substituted allylboronic esters 71 and aldehydes 72 proceed smoothly to give the recovered (R)-71 and (Z)-δ-silyl-substituted homoallylic alcohols 73 with high diastereo-and enantioselectivities, corresponding to selectivity factors up to 328. The authors proposed that the reaction underwent a chair-like asymmetric transition state (TS) through the double coordination of CPA catalyst with the pseudoaxial oxygen-atom of the Bpin motif and the CÀ H bond of aldehyde.…”

Section: Miscellaneousmentioning

confidence: 99%

Recent Advances in (Dynamic) Kinetic Resolution and Desymmetrization Catalyzed by Chiral Phosphoric Acids

Liu

Yang

2021

Asian J Org Chem

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Kinetic resolution, dynamic kinetic resolution and desymmetrization are practical methods to produce enantioenriched products from relatively simple racemic or achiral starting materials, which are also sometimes difficult to be accessed by other asymmetric methods. Chiral phosphoric acids, which have been recognized as one of the most powerful chiral organocatalysts to date, have also been extensively applied in the above-mentioned research fields.In this minireview, we summarized the tremendous development of kinetic resolution, dynamic kinetic resolution and desymmetrization reactions enabled by chiral phosphoric acids since the year of 2016, which were not included in the two previous outstanding reviews by Petersen et al and Dixon et al. A number of examples involving the use of CPA as cooperative catalyst are also included in this review.Scheme 1. KR of β-amino alcohols via CPA-catalyzed p-methoxybenzylations.

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“…In 2021, the Cho group reported a kinetic resolution of α-silyl-substituted allylboronates rac - 168 by chiral phosphoric acid-catalyzed allylboration of aldehydes (Scheme ). Both homoallylic alcohols 169 and α-silylboronates R -168 were obtained with excellent enantiomeric enrichment. The transition state in which the silyl group occupies a pseudoaxial position is favored to minimize steric repulsion between silyl and boryl moieties.…”

Section: α-Boryl Silanesmentioning

confidence: 99%

α-Boryl Organometallic Reagents in Catalytic Asymmetric Synthesis

Zhang

Morken

2021

ACS Catal.

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Recent years have witnessed an increase in the popularity of α-boryl organometallic reagents as versatile nucleophiles in asymmetric synthesis. These compounds have been adopted in chemo- and stereoselective coupling reactions with a number of different electrophiles. The resulting enantioenriched boronic esters can be applied in stereospecific carbon–carbon or carbon–heteroatom bond construction reactions, enabling a two-step strategy for the construction of complex structures with high efficiency and functional group compatibility. For these reasons, tremendous effort has been devoted to the preparation of enantiomerically enriched α-boryl organometallic reagents and to the development of stereoselective reactions of related racemic or prochiral materials. In this review, we describe enantio- or diastereoselective reactions that involve α-boryl organometallic reagents as starting materials or products and showcase their synthetic utility.

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Kinetic Resolution of α‐Silyl‐Substituted Allylboronate Esters via Chemo‐ and Stereoselective Allylboration of Aldehydes

Cited by 17 publications

References 60 publications

Highly Regio‐, Stereo‐, and Enantioselective Copper‐Catalyzed B−H Bond Insertion of α‐Silylcarbenes: Efficient Access to Chiral Allylic gem‐Silylboranes

Highly Regio‐, Stereo‐, and Enantioselective Copper‐Catalyzed B−H Bond Insertion of α‐Silylcarbenes: Efficient Access to Chiral Allylic gem‐Silylboranes

Recent Advances in (Dynamic) Kinetic Resolution and Desymmetrization Catalyzed by Chiral Phosphoric Acids

α-Boryl Organometallic Reagents in Catalytic Asymmetric Synthesis

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